The invention relates to a firing safety for a pneumatic nailer having a pneumatically controlled inlet valve for pressurized air, the valve piston of which inlet valve is, in the non-actuated position of a trigger valve, impinged by pressurized air that escapes, in the actuated position of said trigger valve, through a passageway that exclusively serves for venting purposes.
Several safeties against unintended initiation of a working stroke have become known, as it cannot be excluded that a nail (in the present connection this term includes other drivable fasteners, like in particular staples), which is undesiredly driven into the open air, may cause damage.
It is common to said known firing safeties that they are subject to control by a sensor at the nose-piece of the nailer. A sensing pin projects beyond the underface of the nose-piece and is pressed back when the nose-piece is placed onto an article, usually a workpiece. As long as the sensing pin of the sensor is not depressed, no working cycle can be initiated by means of the manually actuated trigger valve.
For example, it is known from German specification No. 1 503 069 to have the workpiece sensor act on a transmitting lever located between the trigger valve and the manually actuatable trigger lever such that in the non-actuated position of the sensor an actuation of the trigger lever is not transmitted to the trigger valve. In contrast to said purely mechanical firing safety the firing safety known from German laid-open specification No. 21 31 849 engages in the pressurized air control of the inlet valve, in that the workpiece sensor, by moving a cylinder sleeve relatively to the valve piston of the trigger valve, renders the valve seat ineffective even in case the trigger lever is actuated, as long as the sensor is not depressed.
According to German published application No. 22 24 016 there is associated with the trigger valve an identical valve actuated by the workpiece sensor, and a ball valve located between the two valves allows opening of the inlet valve only in case both valves are actuated in concurrence. The same applies to the arrangement known from German laid open application No. 24 53 595, where the workpiece sensor acts on a spring-biased valve located adjacent the nailer nose-piece, which valve prevents, even though the trigger valve is actuated, exhausting and hence actuation of an intermediary valve that controls the inlet valve, as long as a workpiece sensor sensing pin in the form of a valve piston has not been depressed, thereby opening the sensor valve.
It is further common to all firing safeties described so far that the working cycle of the pneumatic nailer can be repeated infinitely, by alternately placing the nosepiece onto a workpiece, and lifting it therefrom, as long as the trigger valve is continuously actuated. In fact, this type of actively controlling the pressurized air inlet valve by means of the nosepiece firing safety is, in operation, often utilized to make use of the firing safety as a trigger valve proper, while the true trigger valve remains constantly actuated. The usual location of the trigger lever below the handle of the nailer aids such use; the said location, while being advantageous manipulatively ergonomically, leads to actuation, and continuing actuation, of the trigger lever when holding the pneumatic nailer. Then the danger exists that a person accustomed to such handling keeps the trigger valve of the nailer actuated even in a condition where the nailer does not rest on a workpiece, and then unintentionally actuates the workpiece sensor, whereby a working cycle is initiated, and a nail is driven out undesiredly.